118 M. Barrande on the Silurian System of Bohemia. 



lower groups. The Cytherinidge have here their maximum, 

 both of numbers (8 species) and size, the latter unequalled 

 either in the extinct or existing creation. The Cephalopods 

 diminish in number, but the Goniatites (3 to 4 species) now 

 appear in forms said to be very analogous to the * Nautilus, 

 and chiefly differing in the dorsal position of the siphon. 

 The Gasteropods and Acephalae have decreased greatly ; the 

 Brachiopods, on the other hand, have now their maximum in 

 107 species {Terebratula 48, Spir if er 22, Leptcena 18, &c.) 

 Encrinites seem also to have been abundant, and the Zoo- 

 phytes, with some old, shew also many new forms, as Bete- 

 pora or Fenestella, Hemitrypa, &c. Nineteen species pass 

 from this into the next higher group. 



The succeeding or upper limestone stage G is distinguished 

 by thicker strata and a more argillaceous composition. The 

 beds mostly consist of nodules of compact greyish limestone, 

 with veins of calc-spar and masses of black chert in their 

 interior. Thin pellicles of argillaceous matter envelope 

 these nodules, and beds of highly laminated slate-clay separate 

 the limestone strata, becoming more abundant and thicker 

 towards the top of the stage. At the same time the lime- 

 stone decreases in amount, and at length terminates in some 

 spheroidal masses intercalated in the slates, in the same 

 manner as it began below. 



Animal life has still farther declined in this stage. Except 

 the Trilobites, all the classes have almost disappeared, and 

 even the remains of the few species that survived are singu- 

 larly indistinct, the shells being, as it were, dissolved into the 

 substance of the rock. The test of the Trilobites is much 

 better preserved, small species being often found in the large 

 chamber of an Orthoceratite, the shell of which has entirely 

 vanished. The following are the genera of Trilobites, with 

 the number of species, — Ilarpes 1, Lie has 1, Calymene 1, Dal- 

 mania 8, Phacops 6, Proetus 5, Gyphaspis 2, Acidaspis 4, Chei- 

 rurus 2, Bronteus 7. It is curious that these are the same 

 genera which appear in the Devonian formations, and espe- 

 cially those of the Rhine and Hartz, where, however, the 

 Calymene and Cheirurus are not certainly known. Only one 

 species of animal, the Phacops foecundus, is common to this 

 and the next stage. 



